This invention relates to an AC adapter for use in a switching power supply circuit or the like.
For example, an AC adapter of the type comprises various electronic parts or components mounted on a circuit board and including a transformer portion, a primary capacitor connected to an input side of the transformer portion, and a secondary capacitor connected to an output side of the transformer portion (for example, see Japanese Unexamined Patent Application Publication (JP-A) No. 2001-268904).
When the various electronic components are mounted on the circuit board, it is attempted in various manners to reduce the size or lower the profile of the AC adapter. For example, with reference to a highest one of the electronic components, the remaining electronic components are designed to be high, thereby reducing a mounting area required to mount the electronic components. Alternatively, with reference to a lowest one of the electronic components, the remaining electronic components are designed to be low, thereby lowering the AC adapter in profile.
However, each of the transformer portion and the secondary capacitor is complicated in shape and requires a large mounting area or a large mounting volume. It is therefore difficult to efficiently arrange those components on the circuit board. Further, relative to an area or a volume available for mounting the electronic components, a number of the electronic components is not small. Therefore, it is difficult to fully respond to a recent demand for a small size and a low profile of the AC adapter.
Referring to FIGS. 1A and 1B, description will be made of a mounting structure of various electronic components in an existing AC adapter (which is not an invention known from a publication but is a generally-used technique).
Most of the electronic components, i.e., three filter portions 21, a primary rectifier circuit portion 22, a switching circuit portion 23, a transformer portion 24, a secondary rectifier circuit portion 25, a primary capacitor 26a, a secondary capacitor 26b, and two voltage change detecting circuit portions 27 are disposed on one surface of a printed circuit board 20. As a remaining part of the electronic components, a control circuit portion 28 is disposed on an opposite surface of the printed circuit board 20 at a predetermined position, i.e., a position substantially faced to one of the filter portions 21.
Upon disposing the electronic components on the printed circuit board 20, a mounting area of the printed circuit board 20 is determined by a total size of mounting surfaces of the electronic components. A height of the AC adapter as a whole is determined by a height of a highest one of the electronic components (herein, the transformer portion 24). Therefore, even if the mounting area of the printed circuit board 20 can be reduced, the height of the AC adapter can not be reduced and a useless space is left. Thus, it is difficult to reduce an external size of the AC adapter as a whole.
Referring to FIGS. 2A and 2B, description will be made of another mounting structure of various electronic components in another existing AC adapter (which is not an invention known from a publication but is a generally-used technique). As compared with the printed circuit board 20 illustrated in FIGS. 1A and 1B, a printed circuit board 20′ has a wider mounting area.
Most of the electronic components, i.e., three filter portions 21′, a primary rectifier circuit portion 22′, a switching circuit portion 23′, a transformer portion 24′, a secondary rectifier circuit portion 25′, a primary capacitor 26a′, a secondary capacitor 26b′, and two voltage change detecting circuit portions 27 are disposed on one surface of the printed circuit board 20′. As a remaining part of the electronic components, a control circuit portion 28 is disposed on an opposite surface of the printed circuit board 20′ at a predetermined position, i.e., a position substantially faced to one of the filter portions 21′.
Each of the filter portions 21′, the primary rectifier circuit portion 22′, the switching circuit portion 23′, the transformer portion 24′, the secondary rectifier circuit portion 25′, the primary capacitor 26a′, and the secondary capacitor 26b′ is designed to have a low profile and is arranged so that the AC adapter has a low profile, as will be understood from comparison between FIGS. 1B and 2B.
However, although the AC adapter as a whole can be reduced in thickness and lowered in profile, the mounting area is inevitably increased because all of the electronic components are surface-mounted on the printed circuit board. It is therefore difficult to reduce an external size of the AC adapter as a whole.